This invention relates to a method for collecting, processing, and analyzing a liquid specimen in a self-contained system. More particularly, this invention relates to an is apparatus and method for collecting, processing, and analyzing liquid specimens in a self-contained system.
Chemical and biochemical analysis of liquids has been traditionally performed in specialized laboratories. However, the classical methods of analytical chemistry have been increasingly replaced by automated analyzers designed for the processing of well-defined specimens. These procedures are typically still conducted in highly specialized institutions by technicians trained in operating particular integrated instruments. In the recent past there has been an increasing trend to develop devices for the analysis of specimens in the field by non-trained personnel to address a specific analytical or diagnostic problem. In fully integrated devices sample collection, processing, and analysis are combined in such ways that they are non-obvious to the user but deliver a final non-coded readout. The degree of integration of all the procedures required for full analysis may vary in the descriptions of prior art.
Several devices and methods have been described to collect liquid specimens by means of fibrous or other absorbent materials for subsequent processing and analysis. Greenspan (U.S. Pat. No. 4,409,988) teaches an apparatus for collecting cultures where the specimen is taken up by the absorbent tip of a swab which is then transferred into a culture medium. In a similar fashion, Nason (U.S. Pat. No. 4,987,504) describes a specimen test unit for which the biological sample is also collected with a swab. For the collection of a specimen for medical diagnosis, Schluter (EP 0 382 905 A2) teaches the use of absorbent material for uptake of liquid and simultaneous separation of particulate matter. In yet another invention describing the collection of a body sample, Kremer (U.S. Pat. No. 4,635,488), a device with a nib containing porous material for absorption is taught. The focus of Zawydski et al's teaching (EP 0 354 704) is on a device for expressing liquid absorbed on a medical swab. A number of devices have been described for collecting oral fluid using an absorbent pad and extracting the fluid from the pad either with a barrel-piston arrangement (U.S. Pat. Nos. 4,418,702; 4,580,577; 4,774,962; 5,056,521) or by centrifugation (U.S. Pat. No. 4,774,962).
All of these applications teach the use of absorbent material to take up a liquid to be analyzed. However, these methods of specimen collection have distinct limitations in a number of applications. Some of these application include, for example:
1. Absorption of molecules or components by the large surface area of absorbent materials if these molecules or components are to be quantitatively analyzed or if they are in a low concentration so that qualitative analysis is impaired (i.e., interference of non-specific binding).
2. Destruction or modification of molecules or components from the liquid to be analyzed by the absorbent materials (e.g., hemolysis of red blood cells in whole blood specimens, catalytic reactions, chemical reactions, etc.)
3. Inaccurate volume uptake, particularly for small volumes (e.g. microliters) and for viscous liquids (e.g. whole blood).
4. Adjustment of hydrophilicity/lipophilicity between the absorbent material and the liquid to be taken up (i.e., non-wettability).
5. Limited capability for expression/desorption of liquid taken up by absorbent materials, particularly for highly viscous liquids (i.e., incomplete recovery of liquid).